Apparatus for the reception of radio messages



June 23, 1931. w Q BARNES 1,811,420

APPARATUS FOR THE RECEPTION OF RADIO MESSAGES Filed Dec. 27, 1926 2Sheets-Sheet 1' June 23, 1931. w. o. BARNES 1,811,420 I APPARATUS FORTHE RECEIITION OF RADIO MESSAGES Filed Dec. 27, 1926 2 Sheets-Sheet 2 II'I I I J I I I I F H!!! "mu "ifi 'www MIHMHHHNHIII HJYwW WZZ: ow: QZone 2a w, azfsawr Patented June 23, 1931 WILLIAM O. BARNES, OFWORCESTER, MASSACHUSETTS APPARATUS FOR THE RECEPTION OF RADIO MESSAGESApplication filed December 27, 1926. Serial No. 157,122.

My invention relates specifically to automatic devices for reducing ornullifying the effects on a radio receiving system of the phenomenoncalled fading, commonly occur rin in long distance reception.

1%hile my invention may be usefully employed in the reception of otherforms of signals, consisting of high frequency electric waves, it is ofspecial value in the reception of 1 radio telephonic communications. Inthe following specification, my invention is shown applied in differentways to radio telephonic receivers, but I do not wish to be limited toits application to that particular branch of the art.

The nullification of the effects of fading is accomplished by theemployment of a novel regulating device, which automatically combineswith each high" frequency wave comprising the signal, a regulating waveof similar form and of an intensity determined by the intensity of thesignal wave and by the mean intensity of all the waves comprising thesignal received during an immediately preceding interval-oftime, therebyaugmenting or diminishing the intensity of each signal wave according asthe mean intensity of the waves received during the immediatelypreceding time interval has been less -or greater than a definiteintensity. This definite intensity is hereinafter called the criticalintensity. j

Reference is to be had to the accompanying drawings in which Fig. 1 is aperspective view of the regulating device, hereafter called the bridge.Figs. 2 and 3 are enlarged views of parts of the bridge shown insection.Fig. 4 is a diagram showing a preferred arrangement of theamplifyingstages of a radio receiver and manner of coupling therewith myregulating device. Fig. 5 is a diagram showing an alternativearrangement of the amplifying stages of a receiver and my regulatingdevice. Fig. 6 shows diagrammatically an alternative method of couplingthe bridge to the circuits of the receiver. Figs. 7, 8 and 9 aregraphical representations of radio signals or waves.

To a suitableinsulating base 1, Fig. 1, the four spring sheet metalterminals .2, 3, 4 and 5 are secured by means of the screws. Fourresistance elements, R1, R2, R3 and R4 are held in place by theelasticity of the upstanding ears of the terminals and electricallyconnect the terminals with one another.

Fig. 2 is a sectional view showing the construction of'resistanceelements R1 and B3. A very thin walled glass tube, 6, of capillarydimensions traverses the interior of a larger glass tube 7. The bore of6 passes through the closed ends of the tube 7. Suitable metallicclosures, such. as the amalgam plugs 8 are provided for each end of thebore of 6. The conductor ofthis element consists of a conducting fluidfilling the bore of 6, such as a dilute solution of chloride ofpotassium;

or it may consist of a very thin film of metal such as silver,chemically deposited on the inside of the Wall of 6. Hereafter the tube6 and the enclosed conductor will be referred.

to as the filament.

The annular space 9, enclosed-betweenfi and 7 is exhausted of air and ishermetically sealed. The interior of 7 is preferably covered with a filmof silver or platinum. This construction is adopted in order to effectu-"ally prevent loss of heat by the filament except by conduction into theends of 7. Under these conditions of thermal insulation, a very minuteelectric current flowing through the conductor will perceptably raisethe temperature of thefilament. I

If a uniform electric current starts to flow through the conductor ofthe filament the temperature of the filament will immediately begin torise and will continue to rise for a certain time until the temperaturesof the various parts of the filament have been raised above thetemperature of the surrounding air,

by certain amounts dependent on the strength of the current. If thestrength ofthe current then changes, the temperatures of all parts ofthe filament will immediately begin to change toward a new set ofvalues.The extentand promptness of this thermal response of the filament tofluctuations in the strength of the current will depend on theelectrical resistance of the conductor, the length and 'cross section ofthe filament and the thermal capacity and thermal conductivity of thematerials composing the filament. lVith a given combination of thedilierent values that may be given to these dimensions, the meantemperature of the filament will be an approxi mate index of the meanstrength of the current dining the preceding interval. of time and, ingeneral, the prompter the thermal. response of the filament to changesin current the shorter will be that interval of time.

Fig. 3 is a sectional view, showing the construction of the resistanceelements R2 and R4. is a thick walled glass tube of capillary bore.Suitable metallic closures, such the amalgam plugs 8, are provided foreach end of the bore. The conductor of this ele ment may consist of asuitable conducting fluid filling the bore of 10 or it may be a metallicfilm deposited on the inside surface of the wall of 10. It is desirablethat the mate ial composing this conductor shall have a smaller thermalcoeflicient of electrical resistivity than the material composing theconductors of I31 and R3, but this is by no means neces sary, as thematerial of all these resistance elements may be the same. The exterioroi? 10 constitutes a large and efficient thermal radiating surface. Thewall of 10 p a broad. and short conducting path :or the escape of heatfrom the conductor to the radiating surface. Consequently, when acurrent of electricity flows through the conductor of R2 or R4 theresulting rise in tein 'rerature is very small as compared to the riseof temperature produced in the conductor of R1 or R2 by the flow thereinof an equal current.

The four resistance elements R1, R2, R3 and R4, when mounted as shown inFig. 1, and a current flows through them between 2 and 4., form aWVheatstone bridge. There will be no dill'erence of potential betweenand 5 when the product of the resistances of R1 and R3 equals theproduct of the resistances of R2 and B4.

In practice it is often convenient to make the resistance and otherdimensions of R1 equal to those of R3, and the resistance and otherdin'iensions 01" R2 equal to those of R4, although these equalities areby no means es- ;-;ential. It will aid the clearness or" the followingdescription, to assume as I therefor do in the following that theseequalities exist.

R1 and R3 are so made that at equal temperatures, they have a slightlylower resistance than R2 and R4. Therefore a current of a certaindefinite or critical strength flowing; through. the bridge between 2 andl will so raise the temperatures in the conductors of H1 and R3 thatthey will have the same resistance as those of R2 and Rel. Under theseconditions the potential at 5 will equal the potential at 3.

It the current is weaker than this critical stren f'h as soon as stablethermal conditions are established, a difference of potential willdepend on the transmittin instrument exist between 5 and. 3, in the samedirection as that existing between 2 and 4. The value of the potentialditlerence will be nearly proportional to the difference between thesquare of the current and the square of the current actually existing.It the current be stronger than critical stren th, the potential.difference between 5 ant! 3 will he n the. rqiposite direction to thatbetween 2 and 4:.

It the current be a high frequency alternating current of fluctuatingvalue, but of smaller mean value than. that called critical, analternating potential will. be set up between 5 and 3 which is in phasewith the potential between 2 and l. he intensity oi the wave ofpotential between 5 and 3, which results from a single alternation ofcurrent will be nearly PlOPOllTlOllfll to the product ot such currentalternation by the difference between square oi. the critical currentand the mean gs the intensity of the potential wave n 5 and 3 will be anincreasing function of the intensity of the potential wave im- 'l on thebridg 7 between 2 and .1;, and a ("lctilciliil'fl function of the meaninten. 'ty of the pole al wave between 2 and il, during an inn-\ediatelypreceding time interval. If I bridge of four resistance elements such asis shown in Fig. 2, and make the ecnC uctors of R1 and R3 of a liquidwhich has a. large thermal coeliicient of resistivity and thecondiiictors of R2 and Iii of silver which has a relatively smallcoethcient, the result is a working bridge which does not dill'erentialemission of heat. 1 liquid that can. be used is chloride of potas sium.

In order to describe clearly the manner in which my automatic regulatoracts to elimi nate the ei'li'ects of fading in broadcast reception, Iwill proceed to describe the nature of the phenomenon, fading, with theaid ot the graqihs Figs. 7, 8 and f). In the preparation of thesegraphs, for the sake of clearness no attempt has been made to representthe true relative frequencies of the carrier wave, the modulationsimpressed thereon by and of the fluctuations of signal strength whichconstitute fading.

In the intervals of silence, during telephonic broadcasting, thetransmitting instru ment will radiate the rapidsuccession of electricalwaves of uniform intensity represented by the sinusoidal line 11, Fig.7. The intensity or strength of these waves is represented by thedistance between the parallel straight lines 12 and. 13 drawn throughthe peaks of 11. When sound affects the transmitter, the waves radiatedare modulated, some are increased in intensity and others decreased. Theresult illustrated in Fig.

S. The lines 14 and 15 are drawn through the peaks of -11 aresinusoidal, the frequency of t eirundu'lations being the same as thefrequency of the sound vibrations affecting the transmitter. If each ofthe waves of 11 be measured, the means or average intensity of all largegroups of successive waves will be found to be practically constant andequal to the distance bet-ween the lines 12 and 13 asinFig/Tw If theintensity-of the waves of 11 be measbetween the lines 12 and 13 at thatplace, or

time, is substantially the same as the ratio between the heightof thesame wave shown in Fig. 8 and the constant distance between the straightlines 12 and 13, which represents the constant mean intensity of thewaves, near the transmitter.

Consequently if to each of the waves comprising .the signal, aregulating wave be added, of like form and frequency, of an intensityproportional to the intensityof the signal wave and of such value as tomaintain the mean intensity of the augmented signal nearly.constant, theform of' the augmented signal will agree closely with that ofthe signalas originally transmitted.

, Fig. 4 illustrates, by means of conventional symbols, one method onincorporating my regulating bridge in a radio broadcast receiver. Thesignal is collected by the antenna A, from which it passes through twostages to tuned radio frequency amplification, consisting of the vacuumtubes Vl'and V2 and their associated circuits. These circuits need noextended. description as they are examples of well known and establishedpractice in coupling the various stages of radio frequency amplifiertogether. Any other known .method of coupling these stages may besubstituted therefor. v.

The plate current fromV2 passes through the inductance L5. This coil ismagnetically coupled to the coil L6 and the signal is delivered'to thegrid of V3. The inductance of vchoke coil L8 is, an efficient barrier tothe passage of the alternating component ofthe plate filament currentfrom V3. Its resistance is sufliciently low, however, to permit thebattery B to maintain sufficient potential on the plate of V3 to insureefficient working of the tube. The alternating component of the currentpasses through condenser C5 and the signal is delivered to the grid ofV4. The

alternating component of the plate-filament current from V4, unable topass throu h the choke coil L9, asses through the con enser C6 andythebri ge resistance R1, R2, R3 and R4. Italso affects the grid: of detectot b V 5], through the condenser C7. i The combination of the two tubesV3-iand V4 will hereafter be referred to as. the regu lated amplifyingelement of the receiver.

The input circuits associated with the tubes 5 V3 and V4 of theregulated amplifying element are shown in the drawings as being of theuntuned variet but it is to be understod that any or al of these inputcircuits be of the tuned variety.

the signal asdelivered by the tuned radio frequency amplifier is of suchintensity.

when multiplied by the normal amplifying powers of V3 and V4, as tocause an alternating current of critical strength to flow through thebridge, no potential will be developed between 5 and 3 and the bridgewill exert no influence on the intensit of the amplified signaldeliveredto the gr1d of the detector.

tential between 5 and 3 will flow through the bridge and the inductancecoil L7. f L7 is magnetically coupled t o L6. Hence the cur rent in L7will cause an augmentation of the signal at the grid of V3. "Thestrength of the current flowing through. the bridge, between 2 and 4,will depend on the amplified intensity of the augmented signal, henceits decrease from critical valueand the decrease in the intensity of thesignal delivered to the detector grid willbe less, proportionately, thanthe decrease in the mean intensityof the incoming signaL. I a i I Whenthe mean intensity of the incoming signalincrea'ses throughTcriticalvalue to something more than critical value the potential waves between5 and 3.willdecrease in intensity through zero tonegative values.

The resulting current throughl? will therefor cause the signal at. thegrid of V3 to be diminished." The strength of the current flowingthrough the bridge, between 2 and 4, will depend on the amplifiedintensity of the diminished signal. of the bridge current between 2 and4 and the intensity of the 'signaldelivered to the grid of the detectorwill be smallemproportionately than the increase in the incoming si al.V

The regulated amplifying element, here shown as consisting oftwof vacuumtubes,

may, in fact, be composed ofany number of tubes. In general, it is foundthat the higher the total normalamplifying power of the tubes composingthis element, the less will be the fluctuation of mean signal intensity,de-

-livered to the detector grid. The human ear is not very sensitive tomoderate fluctuations in the intensity of sound, so that in most casesBut when the signal sinks below this intensity, an alternating currentdue to p0:

Consequently. the increase lol satisfactory reception will be obtainedwith a regulated amplifying element of moderate power.

The selective function of this receiver is shown as performed by twostages of tuned radio frequency amplification. lVhen excessive fading ofthe signal is to be expected, it is advantageous to employ as manysharply tuned stages as possible.

Fig. 5 represents an alternative way of combining the regulatedamplifying element with the other parts of the receiver. The parts ofthis receiver are lettered the same as those in Fig. 4 which performsimilar functions. The incoming signal, instead of passing from thetuned amplifying stages through the regulated amplifying element to thedetector, passes direct from V2 through condenser C5 to the grid of thevacuum tube V6,

thence through condenser C8 to the grid of detector V5. Terminal 2 ofthe bridge is connected to the grid of V6, terminal 4 to the filament ofV2. Terminals 5 and 3 are con nected to the ends of coil L7 which ismagnetically coupled to L6, the grid coil of V3 the first tube of theregulated amplifying element. Consequently, when the mean incomingsignal at 2 is of less than critical intensity, the resultingalternation of potential between 5 and 3 will, acting through V3 and V4cause an augmentation of the signal at the grid of the detector V5.Likewise, when the incoming signal at 2 is of greater mean intensitythan critical value, the resulting potential be tween 5 and 3 will causea decrease of signal intensity at the grid of V5.

Fig. 6 is a diagram showing part of a receiver, in which the bridge iscoupled to the output of the regulated amplifying element by magneticinduction and the compensating increment is added to the signal througha capacity.

The signal is received at the grid of V3, the first tube of theregulated amplifying element, from the plate of the last stage of tunedamplification, (not shown) through the condenser CS. It passes throughthe tubes V3 and V4 as previously described. The output currentof Vetflows through coil L16, which is coupled magnetically to the coil L17.An alternating current is therefore induced in L17, which flows throughthe bridge from 2 to 4 and also affects the grid of the detector V5. Analternating current, due to any potential that may be developed between5 and 3, flows through condenser C9, resistance R7, condenser C10 andthe bridge, and in so doing, increases or diminishes the intensity ofthe signal at the grid of V3, according to whether the mean intensity ofthe incoming signal is deficient or excessive.

It is obvious, that with the magnetic coupling here shown between theoutput of the regulated amplifying element and the bridge, I may alsoemploy the magnetic coupling between the bridge and the input of theregulated amplifying element shown in Figs. 4 and 5.

Carried out in any of the ways shown, it Will be seen that thisinvention provides for compensating for any reduction in the loudness ofthe reception of radiomessages or fading, as it is commonly called. Thisresults in the practically instantaneous increase in the loudness ofreception which, whether entirely compensating for the fading or not,will greatly improve the reception. Incidentally it also cuts downparticularly loud reception and makes the whole message more uniform inthis respect. It is particularly adaptable for radio telephonic messagesbut is of value in all kinds of radio receiving.

Although I have illustrated and described certain forms of apparatus anddiagrams of wiring I am aware of the fact that the invention is notlimited to these particular features and that they can be modified byany person skilled in the art without departing from the scope of theinvention as expressed in the claims. Therefore I do not wish to belimited in these respects but what I claim 1s 1. In a receiving devicefor signals transmitted in the form of electric waves, the combinationwith means for receiving the waves and a regulated amplifying element,of four resistances connected together in the form of a lVheatstonebridge, two opposite terminals of said lVheatstone bridge beingconnected with a receiving circuit, the other two opposite terminalsbeing connected with the amplifying element to vary the intensity of thecurrents therein, the opposite resistances in each case beingconstructed to heat up at different rates under the influence ofelectric current and thus change their relative resistance, the fourresistances constituting means whereby when the intensity of thereceiving current decreases the intensity of the currents through theamplifying element will increase and viceversa.

2. In a receiving apparatus of the class described, an amplifyingelement, an output circuit of the amplifying element composed in part ofa thermally variable resistance so related to other parts of thecircuit, that each signal wave, in passing through the circuit, willgenerate between two points of the circuit, a potential wave of a formsubstantially similar to the signal wave and of an intensity determinedby the intensity of the signal wave and the mean intensity of the signalwaves received during an immediately preceding time interval.

In a. receiving apparatus of the class described, an amplifying element,an input circuit of the amplifying element composed in part of athermally variable resistance so related to the other parts of thecircuit, that each signal wave, in passing through the circuit, willgenerate, between two oints of the circuit, a potential wave of a 01msubstantially similar to the signal wave and of an intensity determinedby the intensit of the signal wave and the mean intensity 0 the signalwaves received during an immediately preceding time interval.

4. A method of controlling the reception of signals composed of electricwaves, which consists of causing such wave of the signal to effect thegeneration of a wave of potential of like form to the signal wave and ofan intensity determined by the mean intensity of the signal wavesreceived during an im mediatel preceding time interval and combining t egenerated wave with the signal wave.

In testimony whereof I have hereunto afiixed my signature. 7

WILLIAM O. BARNES.

